This invention relates to the field of electrography and, more particularly, to magnetic brush development apparatus for applying a magnetically attractive developer to a latent electrostatic image to effect development thereof.
It is known, in the field of electrography, to develop electrostatic images by applying a magnetically-attractive, single-component, electrically conductive developer thereto. Typically, such developer is applied to the electrostatic image-bearing surface by means of a magnetic brush applicator comprising a non-magnetic sleeve having a rotatably driven, multi-pole magnetic core positioned therein. During development, the electrostatic forces associated with the latent image overcome the magnetic attraction between core and developer, causing the developer to selectively deposit in image configuration on the recording element. The attraction of the developer for the electrostatic image results from a charge, of opposite polarity, induced on the developer by the charge image.
In developing electrostatic images with single-component developer, an image defect known as "trailing-edge development" may arise. Such a defect is characterized by a deposition of a small amount of developer in a short region (e.g., 2-4 millimeters in length) beyond the trailing edge of a developed image area. This undesirable deposition of developer occurs after development of the electrostatic image, as the developed image exits from the development zone. At this time, the magnetic developer is still influenced by the rapidly changing magnetic field produced by the rotating magnetic core of the brush applicator, the result being that developer is drawn from within the boundary of the image area and applied to the non-image areas. While this trailing-edge development defect can be minimized by adjusting certain development parameters, e.g., development electrode bias, such an approach has the undesirable effect of altering the sensitometric properties of the development system.